In mounting semiconductor devices on headers problems may arise in the accuracy of alignment of the semiconductor device relative to the header. In particular, high power semiconductor lasers must be mounted such that the laser's far field radiation pattern is not distorted and, additionally, such that adequate heat dissipation is provided.
A semiconductor laser typically comprises a body having a pair of opposed end faces with at least one emitting end face. The body includes a substrate having a buffer layer thereon, a first cladding layer overlying the buffer layer, an active region overlying the first cladding layer, a second cladding layer overlying the active region and a capping layer overlying the second cladding layer with electrical contacts to the substrate and capping layer. Primarily, heat is generated in the active region which is typically in the shape of a ridge which may be three micrometers (.mu.m) or less in width in the lateral direction, the direction in both the plane of the layers and the end faces.
When the laser is mounted to a surface of a header, the emitting end face must be coplanar with, or extend past, the leading edge of the header to prevent reflections of the laser light from the surface of the header which would distort the laser's far field radiation pattern. Generally, heat sinking requirements necessitate that the emitting end face extend no greater than 2 .mu.m past the edge of the surface of the header. As a practical matter these tolerances are difficult to meet since the edge of a standard header, viewed microscopically, is rough and thus requires polishing to obtain a smooth perpendicular edge for mounting. This polishing removes the plating finish on the header which necessitates additional plating operations entailing further time and expense.
After the polishing and plating operations, the laser is soldered to the header. Standard semiconductor device soldering methods are undesirable since these methods place the device in the middle of molten solder and thereby displace solder around the edges of the device. The surrounding solder typically shorts various semiconductor layers, since a high power laser is typically mounted such that the electrical contact opposite the substrate is soldered to the header and the semiconductor layers are of minimal thickness. Consequently, the surface of the header is typically wetted with a thin layer of indium solder and then the laser is gradually positioned on the surface so that the emitting end face is coplanar with the leading edge of the header surface.
These problems demonstrate that it would be desirable to have an economical and efficient method for mounting semiconductor devices on headers.